This invention relates to a valve operating mechanism for an internal-combustion.
It is known to operate charge cycle valves of an internal-combustion engine in a variable manner, that is, with different valve timing and/or lifts. In European Patent Document EP-0 267 687 B1, a valve operating mechanism is disclosed in the case of which two intake valves are operated by means of a camshaft provided with different cams with the insertion of transmission elements constructed as rocker arms. Inside the rocker arms, axially displaceable pistons are disposed which, depending on their position, couple the rocker arms with one another in a form-locking manner. When the piston has moved out, a cam with a large valve lift will actuate the valves by way of two outer rocker arms which are coupled to a center rocker arm. When the piston has moved in, the center rocker arm is uncoupled, and the valves are actuated by way of the outer rocker arms by means of cams with a smaller valve lift.
An arrangement of this type requires a lot of space and is heavy because, in addition to the camshaft, additional shafts are arranged for the bearing of the rocker arms.
It is an object of the invention to simplify an arrangement of the above-mentioned type in a space-saving manner.
This object is achieved by means of an arrangement wherein the transmission elements are formed by the cams with at least one fixed cam non-rotatably connected with the camshaft and at least one rotational cam rotationally arranged on the camshaft and serving as a shift cam. In this valve operating mechanism, the cams are constructed as transmission elements. The construction is compact and one cam is non-rotatably arranged on the camshaft and the other cam is rotatably arranged on the camshaft. The cams act directly upon the valves, and according to the position of the pistons, the non-rotatably arranged or the form-lockingly coupled rotatable cam selectively act upon the valve.
As a result of the design of the cams, which at the same time serve as transmission elements, no rocker arm shafts or the like are required. The space requirement corresponds to a conventional valve operating mechanism in the case of which the cams act directly upon the valves.
By means of one preferred embodiment with the arrangement of three cams situated next to one another on the camshaft, of which the center cam or the two outer cams may be connected or disconnected, the charge cycle valves may be operated by means of different cam profiles.
When the center cam can be connected and is provided with a larger lift, for example, two valves actuated by way of a common tappet are operated in the upper load range of the internal-combustion engine in such a manner that an improved charge cycle will take place.
An arrangement of three cams with an identical lift but with different profile dimensions makes it possible to provide, for example, a shift cam arranged in the center with a course of the valve lift that is optimal for the partial-load range. In order to reduce the occurring friction losses, the shift cam may in this case run up on a roller integrated in the tappet. The center arrangement of a fixed cam with a smaller lift permits a position of the shift cams connected at high rotational speeds which is advantageous for the tappet with respect to stress.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.